Tasty Recipes uses the "thumbnail" image that WordPress automatically creates as the recipe card thumbnail. The size is set in Settings → Media in your WordPress dashboard.
To resolve the issue, you'll first want to check your thumbnail size to see if it's set to a square image—the default is 150x150px.
If it is a square image, but the thumbnail is showing a non-square image, that's usually because the image was uploaded at some point when the thumbnail image wasn't square, and later it was changed to be square.
That said, if you'd like to use a non-square image, you will need to modify the CSS for the recipe card as the non-square image may or may not look good in the card.
When thumbnail settings are changed, thumbnails aren't regenerated for previously uploaded images, so you'll have to use a plugin like Regenerate Thumbnails to make all the new thumbnails.
Alternatively, you can try uploading a brand new image and then selecting that as the recipe image if you don't want to go through the Regenerate Thumbnails route. This is a great way of testing to see if the previous thumbnail size is causing the issue here!